Revert "Airing instead of On Air"

This reverts commit 5b226a4a5e.

UI/Calendar/CalendarLayoutTemplate.html

@@ -8,7 +8,7 @@
         <div class="legend">
             <ul class='legend-labels'>
                 <li><span class="primary" title="Episode hasn't aired yet"></span>Unaired</li>
-                <li><span class="warning" title="Episode is currently airing"></span>Airing</li>
+                <li><span class="warning" title="Episode is currently airing"></span>On Air</li>
                 <li><span class="danger" title="Epsiode file has not been found"></span>Missing</li>
                 <li><span class="success" title="Episode was downloaded and sorted"></span>Downloaded</li>
             </ul>